I would also recommend having a look at the Mayan Adventure Catamaran tour
. Its an incredible tour along the coast line of the Riviera Maya, snorkeling and spot at a private/secret beach that has a Mayan ruin, not huge but really beautiful. The coast line is incredible and the water was gorgeous.
We went on this trip last month on the Holiday and it was a great time. All drinks are included and we drank a bunch of Sole and rum and cokes. Its a pretty good deal and our kids were 1/2 price which was nice. We also go to see this place called Tie Die Island, interesting story there.
Don't forget to try the net boom ride, refreshing and fun!!!
The leave from Porto Venchas about 10 minutes away by cab and the area is beautiful. We stayed around there for a while after the trip to explore before heading back to the ship.